Dimensioning system

ABSTRACT

The present invention provides a dimensioning system for determining the minimum size box necessary to enclose an object traveling on a moving conveyor. The dimensioning system is comprised of a light source which generates a scan beam that is moved by a mirrored wheel. A line scan camera whose field of view tracks the moving scan beam receives images of the scan beam and outputs a signal which is processed to compute a three dimensional box structure of the scanned object.

This application is a continuation of application Ser. No. 08/459,342,filed on Jun. 2, 1995, now U.S. Pat. No. 5,661,561.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for determining thedimensions of an object. More particularly, it relates to a dimensioningapparatus for determining the minimum size box necessary to enclose anobject. Most particularly, the invention is directed to an automaticdimensioning system which accurately determines the dimensions of anobject on a moving conveyor for package sorting and handlingapplications.

2. Description of the Prior Art

In order to reduce costs and increase the volume of packages handled,the shipping industry has pressed automated package handling. This hasbeen accomplished through automated package identification by bar codelabeling and automated sortation by scanners identifying the labels androuting the packages. Package sorting is typically done based on thepackage size. In the shipping industry, shipping fees are directlyrelated to the package size, weight and shipping destination.Determining the correct package size in an efficient manner is thereforeespecially significant for both throughput and fee calculation.

While some progress has been made to provide automated systems forcreating a three dimensional rendering of the package, the known systemsare both complex and costly. There are several known systems forobtaining package dimensions. One system, shown in U.S. Pat. No.5,193,120, utilizes a light source which projects collimated lines oflight onto the object to be measured. An imaging system, utilizing avideo camera, views the object at an angle with respect to thestructured light so that the profile of the object can be visualized.The video signal is processed to calculate the three dimensionalrendering of the object based on the lines of light.

Another system, shown in International Publication Number WO 94/27166,uses a laser beam which is reflected. in a fan shaped form and directedusing mirrors to a flat surface. The laser beam is oscillated at a highfrequency where the difference in phase between the originating beam andthe reflected light off of the surface of an object yields the height ofthe object. The system calculates the time it takes for the light beamto travel to and from the object. The system is mounted in a moveablecarriage which passes over the object and after a multiplicity of heightmeasurements determines the dimensions of the object.

U.S. Pat. No. 4,758,093 discloses a three-dimensional measurement systemwhich uses a holographic scanning mechanism. Triangulation based uponthe projector to camera and relative angles provides the foundation forcomputing the surface coordinates.

An apparatus which determines an object's height is shown in U.S. Pat.No. 4,929,843. This system utilizes a laser beam which is rasteredacross a conveyor surface creating a light stripe. A television camera,having a defined field of view, views the object at an angle causing theapparent location of the light stripe to move based on the objectheight.

Although the known systems can be used to obtain an object's height orto provide a three dimensional rendering, both systems view the objectarea at an angle, then produce a large analog video signal which must befiltered and processed. In order to increase the efficiency and reducethe cost of a dimensioning system, it is desirable to have a low cost,automated means for providing an accurate, high speed rendering of anarticle as it is carried on a conveyor. This object can be accomplishedby reducing amount of visual data processed.

SUMMARY OF THE INVENTION

The present invention provides a dimensioning system for determining theminimum size box necessary to enclose an object traveling on a movingconveyor. The dimensioning system is comprised of a light source whichgenerates a scan beam that is moved by a mirrored wheel. A line scancamera whose field of view is also moved by the mirrored wheel receivesimages of the scan beam and outputs a serial analog waveform which isprocessed to compute a three dimensional box structure of the scannedobject. Further processing is necessary for those objects that havecomplex curves.

It is an object of the invention to provide a dimensioning system whichscans a three dimensional object on a moving conveyor belt andcalculates a box capable of enclosing the object.

Other objects and advantages of the system will become apparent to thoseskilled in the art after reading the detailed description of a presentlypreferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a dimensioning system in position abovea conveyor;

FIG. 2 is a section view along line 2—2 in FIG. 1;

FIG. 3 is a view along line 3—3 in FIG. 1;

FIG. 4 is a view along line 4—4 in FIG. 1;

FIG. 5 is an explanatory diagram which indicates how the offset distanceis measured and the height of the object is calculated;

FIG. 6 is a block diagram of the system;

FIG. 7 is a flow chart of the enclosing process; 20FIG. 8A is anillustration of how the enclosing process determines the first fourpoints;

FIG. 8B is an illustration of how the enclosing process determines thesecond four points;

FIG. 8C is an illustration of how the enclosing process boxes a boxstructure;

FIG. 8D is an illustration of the examine objects phase;

FIG. 9 is a perspective view of an alternative embodiment of thedimensioning system; and

FIG. 10 is a perspective view of a second alternative embodiment of thedimensioning system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment will be described with reference to the drawingfigures where like numerals represent like elements throughout.

A dimensioning system 15 in accordance with the present invention isshown in FIG. 1. The dimensioning system 15 is positioned above aconveyor section 12 carrying an object 14. The dimensioning system 15 iscomprised of a main unit 10 and a parabolic reflecting surface 26. Thedimensioning system is mounted on a stand 16 above a conveyor section 12carrying an object 14. The main unit 10 is enclosed in a housing 18which is made by conventional means of sheet metal or molded plastic.Only a portion of the housing 18 is illustrated in order to show thecomponents of the dimensioning system 15 contained therein.

The dimensioning system 15 is comprised of a laser diode and lensassembly 20 mounted in the housing 18. The laser assembly 20 produces acoherent, collimated beam 21 which is directed toward a six-sided,multi-faceted mirrored wheel 22. The mirrored wheel 22 is driven by amotor 24, which moves the beam 21 as it is reflected from the turningmirrored wheel 22. This produces a series of continuous beams, whichhave been graphically represented by 21 a, 21 b and 21 c. The series ofbeams 21 a, 21 b and 21 c are directed toward a high quality, parabolicreflecting surface 26 which reflects the series of beams 21 a, 21 b and21 c to produce a scan of the conveyor belt surface 13 normal to thedirection of travel.

As graphically illustrated in FIG. 4, the parabolic surface 26 is usedto produce parallel beams 21 a′, 21 b′, and 21 c′ from the mirroredwheel 22 and direct them onto the conveyor belt 13. The mirrored wheel22 is located at the focus of the parabolic reflecting surface 26. Ifthe laser beam 21 is moved directly from the mirrored wheel 22 to thebelt 13, the scan beams would radiate from a point source and castshadows from adjacent objects onto each other. By making the scan beamsparallel from above, no shadowing occurs.

In the preferred embodiment, the laser diode/lens assembly is aMitsubishi 35 mW, 690 nm laser diode with an aspheric glass lens havinga 6.24 mm focal length. Referring back to FIG. 1, the motor 24 and themotor control circuitry 25 is designed to minimize motor drift. In thepreferred embodiment, the motor speed is constantly 533 rpm.

A CCD (charged coupled device) line scan camera 30 is mounted in thehousing 18 and directed toward the mirrored wheel 22. The camera 30 hasa line field of view 42. As the mirrored wheel 22 turns, the line fieldof view 42 is directed to corresponding positions (represented as 42 a,42 b and 42 c) with the series of scan beams 21 a, 21 b and 21 c. Thecamera 30 outputs a serial analog signal to the logic processor 35mounted in the housing 18.

The mounting geometry of the laser assembly 20, camera 30, mirroredwheel 22 and parabolic reflecting surface 26 is shown in detail in FIGS.2-4. The laser assembly 20 and the camera 30 are mounted on a planewhich is parallel to the axis of the mirrored wheel 22. As shown in FIG.3, the laser assembly 20 and the camera 30 are offset from each other byan angle θ which is approximately 5°. θ is defined by measuring theangle between the laser beam center 21 and the central axis 44 of thefield of view 42 of the camera 30.

As shown in FIGS. 2 and 4, the mirrored wheel 22 sweeps the laser beam21 across the parabolic reflecting surface 26, with approximately 90° ofthe swept beam 21 striking the parabolic reflecting surface 26. Theparabolic surface 26 reflects the laser beam 21 to provide a series ofparallel beams 21 a′, 21 b′ and 21 c′.

The camera field of view 42 is aligned in the same plane as the laserbeam 21 and is directed at the mirrored wheel 22. As shown in FIG. 2,the central axis 44 of the field of view 42 is reflected by theparabolic reflecting surface 26 to be approximately normal to theconveyor surface. The angle of the parallel laser beam 21′ afterreflecting off of the parabolic surface 26, remains θ from the centralaxis 44 of the camera field of view 42.

The object height 14 at a given point is measured by triangulation usingthe angle θ. The offset angle θ between the laser beam 21′ and thenormal camera view field 42 above the conveyor creates a horizontaloffset d between intercept point 40 a where the laser beam normallyintercepts the conveyor surface and image point 40 b when the laser beam21 strikes an object 14. As shown in FIG. 5, the offset d is captured bythe linear view field 42 of the camera 30. When the intercept point 40 aand the image point 40 b are the same, i.e. when no object is present,the image is oriented to fall at one end of the CCD linear array do. Asan object comes under the scan beam 21, the image point 40b moves towardthe other end of the CCD array based on the object height at thatdiscrete point on the conveyor belt. The calculation of offset d₁ thedistance from d₀, is explained in more detail hereinafter.

The output of the camera 30 is fed to the input of the A/D (analog todigital) converter 32 as shown in FIG. 6. The A/D output is a binarydigital pulse corresponding to the position of the laser spot.

In the preferred embodiment, the line scan camera 30 is a Dalsa modelCL-C3. The lens has a focal length of 170 mm. To maintain focus over a914.4 mm (36 inch) depth of field, the CCD array is tilted at an anglein relation to the median plane through the lens. The angle of tilt isdetermined using the Scheimpflug condition. The angle is dependent onthe focal length of the lens and the plane angle of the object. Theplane angle of the object is projected towards the lens. The medianplane of the lens is extended to intersect the object plane's extendedline. The image plane's line is similarly extended to intersect at thesame point. For the three lines to intersect, the image plane must beangled. The angle that causes the three extended lines to intersect isthe Scheimpflug angle. The angular relationship is achieved by thespacial relationship and orientation between the object on the conveyor,the reflected light path, and lens and CCD array. The CCD array mustthen be slightly offset such that the object sample points are imagedonto the active area of the CCD array. The use of the Scheimpflugcondition allows for a smaller reflected laser spot size over the entiredepth of field. This yields increased resolution.

The CCD array contains 512 pixels. The maximum scan height is 914.4 mm(36 inches), which yields a resolution of 1.778 mm (0.07 inch) perpixel. The camera 30 takes between 28 and 55 microseconds to integrateand clock out: the pixels after integration. 28 microseconds is theminimum amount of time to clock out the signal.

The camera control circuitry consists of a pixel clock and a cycleclock. The cycle clock controls the integration time and the pixel clockcontrols the rate at which the pixels are clocked out. The cycle clockis synchronized with the scans such that it pulses 240 times (per scan)as it moves across the conveyor belt surface (at 6.35 mm (0.25 inch)increments) starting at scan zero (the conveyor belt edge). The pixelclock is synchronized with the A/D converter to admit the serial datastream.

A block diagram of the dimensioning system 15 is shown in FIG. 6. Thecomponents required to output parallel light and to receive the returnlight have been described above.

After the camera 30 receives the return light, the CCD light-sensitivepixels accumulate a charge proportional to the intensity of theexposure. The output is an analog waveform where the voltage isproportional to the intensity of return light. The laser spot can bemodeled with a Gaussian distribution. It is then input to the processor35.

The processor 35 is comprised of an A/D converter 32 which accepts theanalog signal from the camera 30 and outputs a digital signal. Theconverter uses a fixed level comparator circuit to digitize the analogwaveform from the camera 30. In the first stage of the A/D process, theincoming signal is filtered from unwanted noise and amplified. Thefollowing stages provide variable gain. The final section performs theA/D conversion which produces a binary output pulse.

The logic board 34 accepts the binary signal from the A/D converter 32.The signal is a single pulse corresponding to the reflected image pointdetected by the CCD array in the camera 30. When the LVAL output fromthe scanner is set high (a signal that indicates the camera is clockingout its pixels) the leading edge is used as a starting point to measurethe distance to the laser spot pulse. Two 12 bit, 60 MHz counters arestarted at the rising edge of the LVAL signal. The first counter isstopped and stored in memory at the leading edge of the laser spot pulseindicating the laser beam image point 40 b, and the second counter isstopped and stored in memory at the falling edge of the signal. Theprocessor 35 calculates the difference between the edge values and thisrepresents the center of the laser beam image point 40 b. This number isconverted to a distance d that the laser image point 40 b is apart fromthe conveyor intercept point 40 a d₀. Using this distance d and theangle θ, the box height is, calculated.

The height h is calculated by the logic board 34 using the simpletrigonometric relationship:

h=d/tanθ.  (Eqn. 1)

This relationship can be grouped with the conversion of the counters toa distance in one step. By doing this for each point, the center countcan be converted directly to a height. By creating a lookup table, anyvariation between units in processing can be calibrated out.

Each time d is measured, the height h is calculated at that discretepoint. Measurements of the beam image points are taken as the scanprogresses across the conveyor 12 at preferably 0.25 inch intervals.This yields 240 discrete sample image points per scan. A tachometer 37,measures the conveyor belt speed, and based on the scan frequency, thedistance between scans is calculated.

Each sample image point is composed of an x,y,z component. The xcomponent is the distance, in discrete 0.0625 inch increments, obtainedfrom counting the tachometer pulses. The y component is the distance, indiscrete 0.25 inch increments, from the scan zero side of the conveyor.The z component is the object height h, in 0.0625 inch increments, fromthe belt towards the parabolic reflecting surface as measured by thelaser-camera interaction.

As shown in the flow diagram of FIG. 7, once the data is acquired (step50), it is processed to define a box structure. After a scan has beencompleted, the data from the 240 sample points are fed into apreprocessor function (step 51) in the software. The purpose of thepreprocessor is to convert the raw height data from the camera into 0.07inch increments, and to remove calibrated aberrations from the data. Forexample, if sample image point number 5 is always 2 counts larger thanthe average, the data contained in sample 5 will be lowered by 2 counts.

Once the preprocessor has normalized the data, it is fed into arun-length encoder module (step 52). The run-length encoder takes the240 discrete height samples and converts the entire scan into multipleline segments. Line segments are constructed from groups of adjacentsample image points with similar non-zero heights that lie on the samescan line. Each line segment is defined by its starting position on theconveyor belt, length, and height. Line segments are no longer discrete,their components are averages of the discrete points they were builtfrom. As shown in the flow diagram, after the data is acquired, andpreprocessed, the line segments are then passed to the collection phase.During the data collection phase, the incoming line segments areassigned to a particular box structure according to their position tothe previously gathered line segments.

During the collection phase (step 53) individual line segments maycontain information for more than one object. If the data for the secondobject is apparent due to trends in the previously gathered data, theline segment will be broken into two line segments and assignednormally. If the line segment cannot be broken it will be assignednormally to the closest matching box structure, therefore this boxstructure will now contain the information for more than one object, thesplit phase (step 54), and examine object phase (step 64) should removethis extra information later on.

If during a particular data collection period a box structure did notreceive at least one single line segment, indicating the absence of theobject in the current scan line, that box structure is passed to thesplit phase.

During the split phase (step 54), the software examines the outer edgesof the image defined by the box structure. If the split module noticesdrastic changes in the slope of line segments contained in the boxstructure, the module will break the box structure down into multiplebox structures. Each of these box structures will contain taginformation to rebuild the original box structure if the slopes weremisinterpreted. All of this data will then pass to thedata-reduction-unit.

During the data reduction unit phase (step 56), all line segments thatdo not touch the edges of the calculated box structure image aredeleted. This is accomplished by deleting any line segment where the endpoints do not touch or exceed the previous or next scan line segment'send points. This decreases the processing time during the enclosingphase.

The enclosing phase (step 58) encloses the imaged object within thesmallest box structure. To enclose the object, the angular orientationof a first side must be determined and then two perpendicular sides andan opposing parallel side are calculated such that the area within isminimized and contains all of the line segments. In order to determinethe angular orientation of a first side, points are defined from theline segment: data comprising the box structure.

As shown in FIG. 8A, the T point is the beginning of the first linesegment in the box structure, and has the minimum x value. The B pointis the end of the last line segment, and has the maximum x value. The Rpoint is the beginning of the line segment closest to the scan zeropoint, i.e. the minimum y value. The L point is the end of the linesegment farthest from scan zero, i.e. the maximum y value.

After these four points, T, R, B, and L, are determined, line segmentsare computed. For reference, the center of the box structure is taken asthe point midway between the maximum and minimum x and y values.

As shown in FIG. 8B, the line segments {overscore (TR)}, {overscore(RB)}, {overscore (BL)}, and {overscore (LT)} are moved tangentiallyaway from the center until they enclose all of the individual linesegments defining the box structure. The last sample point where each ofthe computed tangential lines touch a line segment of the box structuredefines four new points; TR,RB,BL and LT.

The final part of the enclosing phase involves defining 16 lines, eachhaving its own angular orientation, by the eight points. The first areais comprised of 8 lines defined between each adjacent point, T and TR,TR and R, R and RB, etc. The second eight lines are defined betweenevery other point, TR and RB, RB and BL, BL and LT, etc. and T and R. Rand B. B and L, etc.

Each of the computed lines defines an angle with respect to the conveyorwidth and running length. For example with respect to the line definedby points BL and L as shown in FIG. 8C, an exaggerated line A iscomputed parallel to line BL to L, and is moved in from outside of thebox structure until it contacts a sample point. Line B is computedparallel to line A and is moved in from the side opposite A. Twoadditional lines normal to lines A, B are computed, C, D and are movedin to box the box structure. This operation is performed for each of thesixteen lines computed above. The smallest area computed that enclosesthe box structure is output to the next phase.

A check is performed by calculating the area of the box structure basedon all of the edge points and the area within the lines defining a box.If the two areas are approximately equal (step 59), the box is thenclosed, otherwise the box is sent to a reprocessing phase.

During the reprocessing phase (step 60) any extraneous line segmentsthat are not similar (step 62) to the adjacent segments are adjusteduntil they match adjacent data. The box structure is then passed back tothe enclosing phase. If the box structure has been through thereprocessing phase previously, it passes to the examine object phase.

The examine object phase (step 64) examines the data and recreates asilhouette picture of the object(s) that were scanned. As shown in FIG.8D, box structures reaching this phase are of irregularly shapedobjects, objects touching other objects or objects oriented in such afashion that the standard process could not accurately enclose them.This phase of the process allows for proper enclosure of tires andseparates complex arrangements of touching objects.

The examine object phase (step 64) of the method generates outlines ofthe box structures and examines these outlines looking for corners.Concave corners and corners that indent into the box structures arenoted. The corners are connected to form sides of boxes, and matchingconcave corners are connected to split apart multiple box structureswhere they meet. The new, individual box structures are then enclosedwithin the smallest rectangle possible.

The final step of the process is the close phase (step 66) where the boxdata is displayed and transmitted to a peripheral device.

It will be recognized to those of ordinary skill in the art that theenclosing process can be tailored to specific applications where knownparameters exist. For example, where it is known that only rectangularbox-shaped objects will be scanned, the comparison done in step 59 canbe made based on a higher approximation of equality since the area ofthe box structure based on all of the edge points should nearly equalthe area of the lines defining the box. Additionally, if it is knownthat all items being scanned have a uniform height, but different itemsmay have a significantly different height, the split phase step 54 maybe configured to look for variations in the uniformity of line segmentheight as one way to determine the existence of two box structuresoccurring within the same set of scans.

The software also corrects for offsets in the mirrored wheel facets andfor changes in the measured height which are caused by the unevendistances between the mirrored wheel and the surface of the conveyor. Asshown in FIG. 4, the scan beam length 21 a is greater than the scan beamlength 21 b. This difference in length follows a simple trigonometricrelationship which is programmed into the software.

The memory on the logic board 34 is large enough to store the relevantdata and some of the frequently used program code. In the preferredembodiment, there are four 256K×32 SRAM modules on board. A preferredprocessor for implementing the software is a Texas Instruments TMS320C30CMOS digital signal processing integrated circuit.

An error count is kept to log the number of times a sample had to beeliminated because of multiple transitions. The quality of themeasurement is also recorded. A scale from 1 to 99 indicates theconfidence level that the dimensions are accurate. If there is any doubtabout the dimensions, it will be assigned a lower number. This numbercan be used as a threshold to determine whether the dimensions areaccurate enough to be used for billing.

While the preferred embodiment utilizes a parabolic reflecting surface26, an alternative embodiment could use a transmission hologram 126 tocollimate the laser beam as shown in FIG. 9. A Fresnel lens could alsobe used to collimate and refract the individual laser beams in a scan tobe approximately parallel to one another.

It is also possible to replace the parabolic reflecting surface 26 withtwo flat mirrors to approximate a parallel scan. The scan is dividedinto three parts. The central portion is a direct scan from the mirroredwheel toward the central portion of the conveyor. Because the width ofthe central portion is limited, shadowing is minimized. The other twoportions of the scan will cover the outer portions of the conveyor. Twoflat mirrors are angled above the rotating mirrored wheel. The lighttravels upwards to the mirror and is then reflected down to the conveyorin a near parallel scan. The flat mirrors are approximating the outerregions of a parabola, with the center portion being replaced by adirect scan from the mirrored wheel. This arrangement requires thesoftware to be more complex to correct for the distance and anglechanges caused by the additional mirrors and the divided scan.

It is also possible to replace the parabolic surface 26 with amulti-faceted parabolic surface to approximate a parallel scan. The scanis divided into discrete parts. The light travels upwards to the mirrorsegments and then is reflected down to the conveyor in a near parallelscan. The mirror facets are approximating a true parabolic surface. Thisarrangement requires the software to be more complex to correct for thedistance and angle changes caused by the additional mirrors. In thisalternative embodiment, 479 samples are acquired per scan.

If there is no possibility that more than one object will be presentduring scanning, no reflecting surface is required. As shown in FIG. 10,the main unit 10 may be used solo with no reduction in accuracy. Withonly one object under the system at a time, no shadowing can occur. Inthis situation parallel scanning is unnecessary and the raw, angularscan becomes the preferred embodiment. No external optics are needed andsystem cost and size can be reduced.

While the preferred embodiment uses a line scan camera, an alternativeembodiment could use a PSD (position-sensitive detector). The PSDoutputs a current which is relative to where the reflected laser spot isdetected. The processing of the output is simplified since the outputcurrent relates position without having coefficient luminanceinformation present.

While the present invention has been described in terms of the preferredembodiment, other variations which are within the scope of the inventionas outlined in the claims below will be apparent to those skilled in theart.

We claim:
 1. An apparatus for determining a dimension of an objecttraveling on a moving conveyor, the apparatus having means for moving ascanning beam across the conveyor such that the beam repeatedlyintercepts the object at an angle e relative to a plane extendingthrough the conveyor, the apparatus characterized by: detecting meanshaving a line field of view which maintains a constant orientationrelative to the scanning beam as the beam moves across the conveyor andreceives a reflected image of the beam at a plurality of image points;and means for calculating the object dimension at each image point basedupon the reflected images.
 2. The apparatus of claim 1 wherein thedetecting means is a line scan camera that outputs a signal whichrepresents an object height relative to the conveyor at each imagepoint.
 3. The apparatus of claim 2 further characterized by a processorwhich receives the signal, calculates a value of the height at eachimage point thereby producing height data, stores data from a pluralityof image points, and determines a three dimensional measurement of theobject based on the height data.
 4. The apparatus of claim 2 wherein:said line scan camera has a lens and detector array; said lens anddetector array are mounted in a fixed angular relationship with respectto each other and an image plane defined at said selected location; andsaid angular relationship is the Scheimpflug angle whereby an objectpassing through said selected location is in the scan camera's focusover a depth of field of at least 304.8 mm (12 inches).
 5. The apparatusof claim 4 wherein the depth of field is at least 914.4 mm (36 inches).6. The apparatus of claim 1 wherein the detecting means is aposition-sensitive detector that outputs a current which represents anobject height relative to the conveyor at each image point.
 7. Theapparatus of claim 6 further characterized by a processor which receivesthe output current, calculates a value of the height at each image pointthereby producing height data, stores data from a plurality of imagepoints, and determines a three dimensional measurement of the objectbased on the height data.
 8. The apparatus of claim 6 wherein: saidposition-sensitive detector has a lens and detector array; said lens anddetector array are mounted in a fixed angular relationship with respectto each other and an image plane defined at said selected location; andsaid angular relationship is the Scheimpflug angle whereby an objectpassing through said selected location is in the position-sensitivedetector's focus over a depth of field of at least 304.8 mm (12 inches).9. The apparatus of claim 8 wherein the depth of field is at least 914.4mm (36 inches).
 10. An apparatus for determining a dimension of anobject traveling on a moving conveyor, the apparatus having means fordirecting a scanning beam across the conveyor at a selected locationsuch that the beam repeatedly intercepts the object at an angle θrelative to a plane extending through the conveyor, the apparatuscharacterized by: detecting means having a line field of view whichmaintains a constant orientation relative to the scanning beam as thebeam moves across the conveyor and receives a reflected image of thebeam at a plurality of image points; means in the path of the movingbeams for converting the light from an angular scan to substantiallyparallel moving beams; and means for calculating the object dimension ateach image point based upon the reflected images.
 11. The apparatus ofclaim 10 further characterized by: means for directing the line field ofview parallel to said plane and aligned such that the detecting meansreceives a reflected image at a reference position when the reflectedimage originates at the conveyor; said detecting means detecting theplurality of image points along the moving beam and outputting a signalcorresponding to the image points; and a processor which receives thesignal, computes a distance d that each image point is offset from thereference position and an object height h at each image point, storesdata from a plurality of image points, and determines a threedimensional measurement of the object based on the height data.
 12. Theapparatus of claim 11 wherein object height at each image point iscalculated using the formula h=d/tanθ.
 13. The apparatus of claim 10wherein said directing means and said converting means are a parabolicsurface.
 14. The apparatus of claim 10 wherein said directing means andsaid converting means are a Fresnel lens.
 15. The apparatus of claim 10wherein said directing means and said converting means are a holographiclens.
 16. The apparatus of claim 10 wherein said directing means andsaid converting means are a multi-faceted parabolic surface.
 17. Theapparatus of claim 11 wherein said detecting means is a line scan camerathat outputs a signal which represents the object height relative to theconveyor at each image point.
 18. The apparatus of claim 17 wherein:said line scan camera has a lens and detector array; said lens anddetector array are mounted in a fixed angular relationship with respectto each other and an image plane defined at said selected location; andsaid angular relationship is the Scheimpflug angle whereby an objectpassing through said selected location is in the scan camera's focusover a depth of field of at least 304.8 mm (12 inches).
 19. Theapparatus of claim 11 wherein the detecting means is aposition-sensitive detector that outputs a current which represents theobject height relative to the conveyor at each image point.
 20. Theapparatus of claim 19 wherein: said position-sensitive detector has alens and detector array; said lens and detector array are mounted in afixed angular relationship with respect to each other and an image planedefined at said selected location; and said angular relationship is theScheimpflug angle whereby an object passing through said selectedlocation is in the position-sensitive detector's focus over a depth offield of at least 304.8 mm (12 inches).
 21. A method of determining adimension of an object traveling on a moving conveyor comprising thesteps of: moving a scanning beam across the conveyor such that the beamrepeatedly intercepts the object at an angle θ relative to a planeextending through the conveyor; providing detecting means having a linefield of view which maintains a constant orientation relative to thescanning beam as the beam moves across the conveyor and receives areflected image of the beam at a plurality of image points; andcalculating the object dimension at each image point based upon thereflected images.
 22. The method of claim 21 further comprising thesteps of: directing the moving beam across the conveyor at a selectedlocation; and converting the beam from angular moving beams tosubstantially parallel moving beams.
 23. The method of claim 22 furthercomprising the steps of: directing the line field of view parallel tosaid plane and aligned such that the detecting means receives areflected image at a reference position when the reflected imageoriginates at the conveyor; computing a distance d that each image pointis offset from the reference position and an object height h at eachimage point; and determining a three dimensional measurement of theobject based on the height data.
 24. The method of claim 23 whereinobject height at each image point is calculated using the formulah=d/tanθ.